Earlier this week, Chicago Fire was among several NBC shows that learned they will officially be returning next season. So it’s a good thing the show has plans to heat things up in the last four episodes of the season, which kick off tonight on NBC. How will they do that? Executive producer Matt Olmstead explained when we had him touch on some of our burning questions…

On Shay and Severide’s baby possibilities:
Shay’s interest in having a baby may have seemed to some like a knee-jerk reaction to having her heart broken (again!) by her ex-girlfriend Clarice (Shiri Appleby), but as it turns out, it was much more than that. Now, she and BFF/sperm donor Severide (Taylor Kinney) are actively trying to get a bun in her oven via in vitro fertilization. “And at the end of the season, we get the answer in terms of whether she’s pregnant or not,” Olmstead promises. But trying to get pregnant will come with more than just medical hurdles. “One of the big season-ending surprises we have is that there’s a romantic interest of his who we’ve seen on the show who comes back to [Severide] and it comes at a time when he and Shay are domesticating. That throws a major wrench into the plan to have a child with Shay,” he says. “Someone comes back from his past and throws everything upside down.”

On the (sort of) spin-off:
Just last week, The Vampire Diaries saw great success after airing a backdoor pilot, and in fact, the series in question (The Originals) was picked up to series the day after it aired. Similarly, Olmstead explains that the season-end arc had room for a Chicago Fire episode that introduced more faces from the police department. (See below for more on what brings them into the fold.) So while the penultimate episode will feature more cop characters than usual and could be ordered to a separate series, “we’ve always approached it as a Chicago Fire episode,” he says.

A death is coming:
As you may have read in Spoiler Room, there is a death coming, and it will rock the life of at least one member of the department. That death will be the impetus for pulling more cops into the Chicago Fire world. ”There was certainly some well-founded mistrust from our guys in particular,” Olmstead says, referring to Casey’s battle earlier this season with dirty cop Voight (Jason Beghe). “Now they’re having to lean on them.”

On Hallie’s return:
After several ups and downs in her relationship with Casey (Jesse Spencer), Hallie will reappear in these last four episodes and will reveal herself to be a new woman, says Olmstead. “She does come back into his life and that’s a further complication for that whole [Dawson-Mills-Casey] triangle,” he says. “When she returns, it’s a new Hallie – having found herself and having given it some thought and realizing the old adage of ‘you don’t realize what you got until it’s gone,’ which again, complicates things.”

On the season-ending cliffhangers:
“I’ll tell you, we’re adding definition to some of the triangles and answering some of the questions out there,” Olmstead says of the May 22 season ender. “If you look at our endings [this season], we like to mix it up. There’s the emotional, cathartic ending and the cliffhanger ending in every episode. So we’ve sort of combined that in [episode] 24. We have emotional payoff and answers emotional questions we’ve posed and emotional cliffhangers.” Moreover, he teases the firehouse could be seeing one of its own thinking about a life change. “[There is] the possibility of a character leaving the firehouse, looking for a cleaner slate somewhere else,” he teases.